qnx4: work around gcc false positive warning bug

[linux-block.git] / fs / qnx4 / dir.c

diff --git a/fs/qnx4/dir.c b/fs/qnx4/dir.c
index 2a66844b7ff875e3920b103602d917ebc76aa268..66645a5a35f306bc2213baff61166f03f9cb9e91 100644 (file)
--- a/fs/qnx4/dir.c
+++ b/fs/qnx4/dir.c
@@ -20,12 +20,33 @@
  * depending on the status field in the last byte. The
  * first byte is where the name start either way, and a
  * zero means it's empty.
+ *
+ * Also, due to a bug in gcc, we don't want to use the
+ * real (differently sized) name arrays in the inode and
+ * link entries, but always the 'de_name[]' one in the
+ * fake struct entry.
+ *
+ * See
+ *
+ *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578#c6
+ *
+ * for details, but basically gcc will take the size of the
+ * 'name' array from one of the used union entries randomly.
+ *
+ * This use of 'de_name[]' (48 bytes) avoids the false positive
+ * warnings that would happen if gcc decides to use 'inode.di_name'
+ * (16 bytes) even when the pointer and size were to come from
+ * 'link.dl_name' (48 bytes).
+ *
+ * In all cases the actual name pointer itself is the same, it's
+ * only the gcc internal 'what is the size of this field' logic
+ * that can get confused.
  */
 union qnx4_directory_entry {
        struct {
-               char de_name;
-               char de_pad[62];
-               char de_status;
+               const char de_name[48];
+               u8 de_pad[15];
+               u8 de_status;
        };
        struct qnx4_inode_entry inode;
        struct qnx4_link_info link;
@@ -53,29 +74,26 @@ static int qnx4_readdir(struct file *file, struct dir_context *ctx)
                ix = (ctx->pos >> QNX4_DIR_ENTRY_SIZE_BITS) % QNX4_INODES_PER_BLOCK;
                for (; ix < QNX4_INODES_PER_BLOCK; ix++, ctx->pos += QNX4_DIR_ENTRY_SIZE) {
                        union qnx4_directory_entry *de;
-                       const char *name;
 
                        offset = ix * QNX4_DIR_ENTRY_SIZE;
                        de = (union qnx4_directory_entry *) (bh->b_data + offset);
 
-                       if (!de->de_name)
+                       if (!de->de_name[0])
                                continue;
                        if (!(de->de_status & (QNX4_FILE_USED|QNX4_FILE_LINK)))
                                continue;
                        if (!(de->de_status & QNX4_FILE_LINK)) {
                                size = sizeof(de->inode.di_fname);
-                               name = de->inode.di_fname;
                                ino = blknum * QNX4_INODES_PER_BLOCK + ix - 1;
                        } else {
                                size = sizeof(de->link.dl_fname);
-                               name = de->link.dl_fname;
                                ino = ( le32_to_cpu(de->link.dl_inode_blk) - 1 ) *
                                        QNX4_INODES_PER_BLOCK +
                                        de->link.dl_inode_ndx;
                        }
-                       size = strnlen(name, size);
+                       size = strnlen(de->de_name, size);
                        QNX4DEBUG((KERN_INFO "qnx4_readdir:%.*s\n", size, name));
-                       if (!dir_emit(ctx, name, size, ino, DT_UNKNOWN)) {
+                       if (!dir_emit(ctx, de->de_name, size, ino, DT_UNKNOWN)) {
                                brelse(bh);
                                return 0;
                        }